Lubricating formulations and greases with a wide assortment of different materials are known. For example, lithium complex greases are well known and can be made from any of a wide variety of base stocks of lubricating oil viscosity, as well as mixtures of base stocks. For example, lithium complex greases that comprise a lithium complex thickener and a lubricating base oil are well known. Greases have varied levels of desirable grease characteristics, such as dropping point, penetration, mechanical stability, shear stability, oxidation resistance, high temperature resistance, etc., based on its composition, which may include the use of polymers. The above characteristics are used to describe the lubricating life of a particular grease.
The use of polymers to impart desirable properties to grease is known and widely practiced by grease manufacturers; see, for example, the description of various thickeners in Manufacture and Application of Lubricating Greases (1954), Reinhold, N.Y. 1954 and Alteration of Grease Characteristics with New Generation Polymers, G. D. Hussey, NLGI Spokesman, August 1987. Oil soluble polymers have been used, for example, to increase the structural stability of greases and to confer reduced oil separation, and increased water resistance. Although these benefits could be obtained without polymers by using lubricating oils having high viscosity base stocks, the resulting debit on low temperature mobility (i.e., pumpability) severely limits a non-polymer approach.
Water resistance is a property desirable in grease for many industrial applications; for example, in papermaking machinery and gearboxes, power transmissions and other bearings used in wet environments such as the slewing bearings in large outdoor antenna mountings, steel mills, and cranes on offshore oil rigs. It has been previously found that polymers may be effective in improving the water resistance of industrial and automotive greases. U.S. Pat. No. 5,110,490 (Pink), for instance, describes a grease composition with enhanced water resistance containing an ethylene copolymer with amine functionality. The copolymer is produced by reaction of a polyamine, such as ethylene diamine with an ethylene copolymer grafted with carboxylic moieties by reaction with an unsaturated carboxylic acid or anhydride group, for example, maleic anhydride. Amine functionalized ethylene copolymers of this type are described in U.S. Pat. No. 4,517,104 (Bloch) to which reference is made for a description of them.
High shear resistance is a property desirable in grease for many industrial applications; for example, in papermaking machinery and steel mill machinery. The particular environments, papermaking and steel mill ball bearings, also result in the exposure to high temperatures. The exposure to high shear, high temperatures, and wet conditions accelerate the breakdown process of grease compositions.
Currently, lithium soap based greases represent approximately 80% of the lubricating grease market and generally provide acceptable lubricating performance. However, lithium soap based greases are limited by their resistance to high-temperatures, wet environments, and shear. For example, lithium soap based grease in polyalphaolefin (PAO) based fluid maxes out at 140° C. Currently available high-temperature lithium greases are either composed of solid particles, such as polytetrafluoroethylene (PTFE), which induce wear and tear on the lubricated surface(s) (such as bearings, gears, slide plates, etc.), or polyester (POE) base oils, which are costly, are limited in certain properties and impractical for manufacture.
Polymer additives are well established for enhancing grease performance at low treatment levels as reported in NLGI Paper Benefits of Polymer Additives in Grease, Larson, et al., NLGI Spokesman, ISSN: 00276782, Vol: 73, Issue 7. As discussed in Larson, the challenges facing grease manufacturers face can be addressed with the inclusion of polymer additives in a variety of grease types. The benefits of polymer additives in Larson are shown to include improved shear stability, enhanced water resistance, and increased yield. In addition to performance enhancements, selected polymer additives may provide economic benefits through increased grease yields of up to 17%.
Polymers that have been studied as grease additives include polyisobutylene (PIB), ethylene-propylene copolymers (OCP), styrene-hydrogenated butadiene (SBR), styrene-hydrogenated isoprene (SI), radial hydrogenated polyisoprene (star), acid functionalized polymers (FP), polymethacrylate (PMA), styrene ester copolymers (SE), and styrene ethylene butylene copolymers (SEBCP). These polymers have been used as co-thickeners e.g. with a calcium soap as described in U.S. Pat. No. 5,084,193 (Waynick) or as the sole thickener as in U.S. Pat. No. 5,874,391 (Meijer).
As technology advances and throughput increases with mechanical devices, there is an increased demand for higher temperature operating conditions and lubricating compositions, such as grease, with enhanced resistance. This is further compounded by the need for lubricating compositions that can effectively function in wet, high shear environments. For example, the environment that ball bearings found in steel mills and paper mills is particularly harsh with high levels of moisture, shear, and heat. The working life of grease is limited in such an environment, which results in greater wear on the equipment and longer downtimes as a result of maintenance (e.g., re-greasing the ball bearings and replacement/maintenance of warn parts of the equipment).
Thus, a need exists for lubricating greases that have enhanced/extended high temperature resistance that can be utilized in high shear, wet environments.